Method of determining an object&#39;s position and associated apparatus

ABSTRACT

A method of determining an object&#39;s position and associated apparatus provides positional information in a form that may be conveniently communicated to a computer system to calculate the object&#39;s position. In a disclosed embodiment, representatively incorporated in a computer keyboard, a method of determining an object&#39;s position includes forming an optical grid of overlapping beacons and detecting reflections of the beacons produced by the object when it intersects the grid. The disclosed embodiment utilizes two focused beacons to produce the optical grid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.08/651,881, filed on Jun. 4, 1996, now U.S. Pat. No. 5,786,810, which isa continuation-in-part of U.S. application Ser. No. 08/486,310, filed onJun. 7, 1995, now U.S. Pat. No. 5,734,375.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods of determining anobject's position and, in a preferred embodiment thereof, moreparticularly provides a method and apparatus for optically digitizing anobject's position on a plane above a computer keyboard.

2. Description of Related Art

Pointing devices are well known in the computer art. Their purpose,generally, is to permit a computer user to input positional informationto the computer. A pointing device performs this function by"digitizing" an object's relative position in space, that is, by puttingthe positional information in a form that is readable by the computer.

The number of uses for pointing devices have increased as moderncomputer user interfaces have become increasingly graphical. Forexample, a computer user may now use a "mouse" to select a file to openfor editing purposes (by "clicking" on an icon representing the file),instead of typing a file name on a keyboard.

Typical pointing devices currently available to computer users includemouse, trackball, digitizing pad, joystick, touch screen, and eyetracking devices. There are variations of each of these and there arepointing devices that have a combination of features found on more thanone of these. Each, however, has its disadvantages.

A mouse typically has a housing for grasping in the user's hand, and aball underneath the housing for rolling the housing about on a desktop.Rollers inside the housing digitize the mouse's position by translatingthe ball's movement into electrical signals which are then communicatedto the computer. Switches, typically mounted to the housing's topsurface, allow the user to "click" (activate a switch to select an icon,for example) on an object displayed on the computer's screen, or performother functions. The mouse, however, requires the user to devote asignificant portion of a desktop as an area in which the mouse can berolled around. The mouse also requires the user to remove one hand fromthe keyboard while the mouse is being rolled around on the desktopand/or while a mouse switch is being activated, thus slowing down thedata entry process. Furthermore, the mouse requires a means ofcommunicating the electrical signals to the computer, such as a cablewhich must be attached between the computer and the mouse and mustfollow the mouse around the desktop.

A trackball eliminates some of the mouse's disadvantages, butsubstitutes others in their place. The trackball is, essentially, anupside-down mouse, having a stationary housing with the ball facingupward so that the ball can be rolled by the user's fingers. Theswitches are normally placed on the top surface of the housing adjacentthe ball. The rollers which translate the ball's motion into electricalsignals are located in the housing where, due to the large upward-facingopening in the housing through which the ball protrudes, they areexposed to dust and dirt. Some keyboard manufacturers have eliminatedthe need for a separate trackball device cable for communicating theelectrical signals to the computer by building the trackball devicedirectly into the keyboard housing so that a single cable communicatesboth keyboard and trackball input to the computer. The user does,however, still have to move his or her hand away from the keyboard inorder to roll the ball. Another disadvantage is that a large amount ofdexterity is required to manipulate the trackball while clicking on ascreen object, if only one hand is used.

A digitizing pad typically utilizes a rectangular planar area on thesurface of a hard plastic housing, which, in turn, is placed on theuser's desktop. The pad uses one of several methods to sense theposition of a pen or stylus on the pad surface. In some pads, thepressure of the pen or stylus on the pad surface makes contact orchanges capacitance in many fine, closely spaced conductors beneath thepad's surface. In some others, the pen or stylus carries a magnetic orelectromagnetic field source which is sensed by the pad, thus, the penor stylus position is sensed due to the proximity of the pen or stylusto the pad. Among the digitizing pad's disadvantages is the space on thedesktop taken up by the pad's housing. Additionally, the user mustremove his or her hand from the keyboard to operate the pen or stylus.

A joystick is another pointing device, and may have either a movable ora non-movable stick. The movable joystick operates similar to atrackball, except that a stick is inserted into the ball giving the usera means of grabbing the ball. The stick also limits movement of theball. The non-movable joystick utilizes pressure sensors encircling thestick to sense the force and direction in which the user is pushing thestick. Thus, the non-movable joystick does not communicate a position tothe computer, instead it senses a force vector which the computer mayuse to adjust the position of a screen object. With either type ofjoystick, manipulation of the switches and stick is very difficult withonly one hand, thus, in order to use a joystick, the user must removeboth hands from the keyboard.

Eyetracking devices use expensive, sophisticated methods of determiningwhere on the computer screen the user's eyes are focused. In this waythe user's hands do not have to leave the keyboard in order for thepositional information to be communicated to the computer.Unfortunately, however, this technology is not within financial reach ofmost computer users.

Touch screens permit the user to communicate a position to the computerby actually touching an area on the computer screen. Usually the screenarea is associated with an object or menu choice displayed on thescreen. As with all of the aforementioned pointing devices, with theexception of the eyetracking devices, the user's hand must leave thekeyboard to use the device.

From the foregoing, it can be seen that it would be quite desirable toprovide a method of communicating an object's position to the computerwhich does not require the removal of either of the user's hands fromthe keyboard and which may be economically produced. It is accordinglyan object of the present invention to provide such a method andassociated apparatus.

SUMMARY OF THE INVENTION

In carrying out the principles of the present invention, in accordancewith an embodiment thereof, a method is provided which permits the userto communicate positional information to the computer by reflectinglight beacons in a light grid with the user's finger, without removingeither of the user's hands from the keyboard. An apparatus is alsoprovided which produces the light grid from one or more light sourcesand detects the position of an object reflecting light within the grid.

In broad terms, a method of sensing an object's position is provided,the method comprising the steps of generating a plurality of lightbeacons, sweeping the light beacons across an area, thereby formingalight grid of intersecting or overlying beacons, reflecting the beaconsoff of an object positioned within the grid, and receiving the reflectedbeacons into a plurality of light sensors.

In an optical digitizer apparatus disposed in relation to a keyboardused in a computer system, two light sources are utilized to produce alight grid in a plane above an upper surface of the keyboard. The lightgrid is formed by two beacons which are produced when two light beamsfrom the two light sources are reflected off of two oscillating mirrors.When the beacons strike an object within the grid, the beacons arereflected back to the mirrors, off of two beam splitters, and to twolight sensors.

In one aspect of the present invention, the light sensors may includeimaging or non-imaging detectors. If imaging detectors are utilized, animage recognition program in the computer may permit the object to berecognized by the computer before determining the object's position. Inthis way, extraneous objects will not produce false positiondeterminations.

In another aspect of the present invention, the beacons may be focused,so that the light grid is limited in area and/or shape. This may beaccomplished by inserting one or more lenses in the paths of thereflected beacons. Lenses may also be utilized to restrict a width,height, etc. of the reflected beacons which are received at the lightsensors.

In yet another aspect of the present invention, the position of theobject in the light grid is determined by triangulation, based on theangular positions of the oscillating mirrors when the reflected beaconsare received at the light sensors, and the positions of the mirrors withrespect to each other. In this way, the beacons, reflected off of theobject itself, are used to determine the object's position.

The use of the disclosed method and associated apparatus enablespositional information to be conveniently and economically communicatedto the computer. Use of the computer keyboard device embodiment enablesthe user's time to be more effectively utilized since the user's handsdo not have to leave the keyboard to communicate positional informationto the computer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an optical digitizer;

FIG. 2 is a flow chart illustrating a method of determining an object'sposition;

FIG. 3 is a top plan view of a computer keyboard having the opticaldigitizer of FIG. 1 thereon;

FIG. 4 is a cross-sectional view through the keyboard, taken along line4--4 of FIG. 3;

FIG. 5 is an isometric view of a light grid produced by the opticaldigitizer illustrating obstructed and unobstructed portions of the lightgrid;

FIG. 6A is a plot of light reflected back to a light sensor of theoptical digitizer when the light grid is totally unobstructed;

FIG. 6B is a plot of the light reflected when the light grid isobstructed by an object in a first position;

FIG. 6C is a plot of the light reflected when the light grid isobstructed by an object in a second position;

FIG. 6D is a plot of the light reflected when the light grid isobstructed by an object in a third position;

FIG. 6E is a plot of the light reflected when the light grid isobstructed by an object in a fourth position;

FIG. 7 is a schematic representation of another optical digitizerembodying principles of the present invention;

FIG. 8 is a cross-sectional view through the optical digitizer of FIG.7, taken along line 8--8 of FIG. 7;

FIG. 9 is a top plan view of a partially cut away computer keyboardhaving the optical digitizer of FIG. 7 thereon;

FIG. 10 is a schematic representation of yet another optical digitizer;

FIG. 11 is a top plan view of a partially cut away computer keyboardhaving the optical digitizer of FIG. 10 thereon;

FIG. 12 is a top plan view of a computer keyboard of a computer system,the computer keyboard having still another optical digitizer embodyingprinciples of the present invention disposed thereon;

FIG. 13 is a schematic representation of a modification of the opticaldigitizer of FIG. 12; and

FIG. 14 is a schematic representation of another modification of theoptical digitizer of FIG. 12.

DETAILED DESCRIPTION

Illustrated in FIG. 1 is an optical digitizer 10. It is shown in highlyschematicized form for the purpose of clarity. Dashed lines and arrowsare used to represent paths and directions, respectively, of light.Filled arrowheads represent directions of unreflected light and unfilledarrowheads represent directions of reflected light in a manner that willbecome apparent as the following detailed description is read andunderstood.

A light source 12 provides a compact beam of light 14 which is in theinfrared portion of the light spectrum in the illustrated embodiment.The light source 12 includes a laser 16 which, in turn, includes a lightemitting diode 20 and a collimator 22. The light emitting diode 20produces infrared light when leads 18 are connected to a power source(not shown). The infrared light produced by the light emitting diode 20is made into the beam 14 having essentially parallel sides by thecollimator 22.

The beam 14 next passes into a beam splitter 24. The beam splitter 24includes a half-silvered mirror 26 which passes half of the beam 14 andreflects the other half. The reflected half of the beam 14 is not usedin the illustrated embodiment, so it is not shown in FIG. 1.

The beam 14 next passes into a beacon generator 28. The beacon generator28 produces a beacon 30 from the beam 14 by reflecting the beam 14 offof an oscillating mirror 32. The beacon 30 differs from the beam 14 inthat the beacon 30 "sweeps" across a plane, whereas the beam 14 remainsstationary. In other words, the beacon 30 is the beam 14 put into motionby the oscillating mirror 32.

It is to be understood that the beacon 30 may be generated from the beam14 by another method. For example, instead of the oscillating mirror 32in the beacon generator 28, a rotating polygonal mirror could be used torepeatedly and sequentially sweep beam 14 across an area. As a furtherexample, beam 14 could be directed across a curved surface instead of aflat plane.

The beacon 30 is directed into a beacon separator 34. In the beaconseparator 34, the beacon 30 is separated into several components. Onecomponent is (as viewed in FIG. 1) a horizontal component 36. Thehorizontal component 36 passes through the beacon separator 34 in theillustrated embodiment without any change in direction. Anothercomponent, a vertical component 38 (as viewed in FIG. 1), is reflectedoff of a mirror 40 so that it is directed in a direction different fromthe horizontal component 36.

In the area intermediate the horizontal component 36 and the verticalcomponent 38 of the beacon 30 in the beacon separator 34 is adiscriminating reflector 42. The purpose of the discriminating reflector42 is to allow the optical digitizer 10 to discriminate the horizontalcomponent 36 from the vertical component 38. The discriminatingreflector 42 directs a small portion of the beacon 30 back to theoscillating mirror 32. The manner in which the discriminating reflector42 allows discrimination between the horizontal and vertical components36,38 will become clear upon further description of the embodimentbelow.

The horizontal component 36 of the beacon 30 next strikes a reflector 44which directs the beacon 30 in a downward direction as viewed in FIG. 1.Thus, it can be seen that as the horizontal component 36 of the beacon30 sweeps across the downwardly facing surface of reflector 44, it ismade to sweep horizontally from side to side as viewed in FIG. 1. Theuppermost limit of the horizontal component 36, illustrated as a beam 46in the beacon separator 34, once reflected off of the reflector 44,becomes the leftmost limit of a horizontal beacon portion 48 as viewedin FIG. 1. The lowermost limit of the horizontal component 36,illustrated as a beam 50, once reflected off of the reflector 44,becomes the rightmost limit of the horizontal beacon portion 48 asviewed in FIG. 1. Therefore, the horizontal beacon portion 48 is nothingmore than the horizontal component 36 of the beacon 30 reflected off ofthe reflector 44.

The reflector 44 in the illustrated embodiment is constructed of amaterial which enhances the accuracy of the optical digitizer 10. Thematerial, a reflective angle film (RAF) available from the 3MCorporation, reflects light at the same angle independent of the angleat which the light strikes its surface, within limits. In FIG. 1, it canbe seen that beam 46 strikes the reflector 44 (constructed of the RAFmaterial) at a slightly different angle than does beam 50, however, oncereflected off of reflector 44, beams 46 and 50 are parallel in thehorizontal beacon portion 48. It is to be understood that the reflector44 does not have to be made of the RAF material, and that beams 46 and50 do not have to be parallel in the horizontal beacon portion 48.

The reflector 44 could have a curved shape instead of the linear shaperepresentatively illustrated in FIG. 1. In that way, a beam passing overthe surface of the reflector 44 could be reflected in a direction whichdepends upon the curvature of the reflector 44.

Vertical component 38 of the beacon 30, after leaving the mirror 40 inthe beacon separator 34, strikes a reflector 52 which is made of the RAFmaterial in the illustrated embodiment. A beam 54, farthest to the rightin the vertical component 38 as illustrated in FIG. 1, strikes thereflector 52 and is reflected to the right in a direction orthogonal tothe horizontal beacon portion 48. A beam 56, farthest to the left in thevertical component 38, strikes the reflector 52 and is also directed tothe right, orthogonal to horizontal beacon portion 48 as illustrated inFIG. 1. Thus, it can be seen that vertical component 38 of the beacon 30is reflected off of reflector 52 so that it sweeps vertically, asillustrated in FIG. 1, between the representatively shown beams 54 and56, forming a vertical beacon portion 58 which is orthogonal tohorizontal beacon portion 48. Note that, as with reflector 44 describedabove, reflector 52 could have a curved shape and could be made of othermaterials.

Since beam 14 is continuously directed to the oscillating mirror 32 inthe beacon generator 28, the resulting beacon 30 is also continuous.Therefore, although beams 46 and 50 are illustrated as being at theouter limits of horizontal beacon portion 48, and beams 54 and 56 areillustrated as being at the outer limits of vertical beacon portion 58,it is important to understand that the beam 14, in the form of thevertical or horizontal beacon portion 48,58 sweeps continuously betweenthese outer limits. Note, however, that at any one instant in theillustrated embodiment, beam 14 may be directed to the horizontal beaconportion 48 or vertical beacon portion 58, but not both.

It is also important to note at this point that although separate beams46,50,54,56 are referred to in this description of the illustratedembodiment, no two of these are present at one time, since they allemanate from the same beam 14 produced by the light source 12. Beams46,50,54,56 representatively illustrated in FIG. 1 are all simplydifferent positions of beam 14. Likewise, different beacon portions48,58 and beacon components 36,38 are just parts of beacon 30, which is,in turn, made up of different positions of beam 14 produced by theoscillating mirror 32.

Beam 56 intersects beam 46 at point 60 and intersects beam 50 at point62. Beam 54 intersects beam 46 at point 64 and intersects beam 50 atpoint 66. Since the horizontal beacon portion 48 is orthogonal to thevertical beacon portion 58, points 60, 62, 64, and 66 define the cornersof a rectangular light grid 68. In this light grid 68, the horizontalbeacon portion 48 sweeps from side to side, and the vertical beaconportion 58 sweeps from top to bottom, as representatively illustrated inFIG. 1. For the purpose of further description of the illustratedembodiment, the defined beginning of the sweep of the horizontal beaconportion 48 shall be at its leftmost limit (beam 46 as illustrated inFIG. 1), and the defined beginning of the sweep of the vertical beaconportion 58 shall be at its upper limit (beam 56 as illustrated in FIG.1).

It is to be understood that the light grid 68 could have a shape otherthan rectangular. If, as described above, beams 46 and 50 are notparallel to each other, a trapezoid shape is produced. If, additionally,beams 56 and 54 are not parallel to each other, another polygonal shapeis produced. Light grid 68 may take virtually any shape as long as nobeam in the horizontal beacon portion 48 is collinear with a beam in thevertical beacon portion 58.

Reflector 70, representatively illustrated in FIG. 1 as beinghorizontally disposed at the lowermost extent of horizontal beaconportion 48, reflects the horizontal beacon portion 48 directly back inthe direction of reflector 44. Unfilled arrowheads on beamsrepresentatively illustrated in horizontal beacon portion 48 indicatethe direction of beams which have reflected off of reflector 70. Thus,beams in the horizontal beacon portion 48 are reflected back toreflector 44, thence back through the beacon separator 34 to theoscillating mirror 32 in the beacon generator 28, and thence to the beamsplitter 24.

In a similar manner, reflector 72, representatively illustrated in FIG.1 as being vertically disposed at the right-hand edge of vertical beaconportion 58, reflects the vertical beacon portion 58 directly back in thedirection of reflector 52. Unfilled arrowheads on beams representativelyillustrated in vertical beacon portion 58 indicate the direction ofbeams which have reflected off of reflector 72. Thus, beams in thevertical beacon portion 58 are reflected back to reflector 52, thenceback to the mirror 40 in the beacon separator 34, thence to theoscillating mirror 32 in the beacon generator 28, and thence to the beamsplitter 24.

Reflectors 70 and 72, in the illustrated embodiment, are made of amaterial which reflects light back in the same direction at which itinitially strikes the material. It is known to those skilled in the artas retro-reflecting film. There are several types of retro-reflectingfilm, including micro corner cube and micro sphere. The micro cornercube type has been found to give acceptable results in the illustratedapparatus.

In the illustrated embodiment, with no obstruction blocking the path ofany beam, the cumulative total of the beams reflected back from thehorizontal and vertical beacon portions 48,58 and the discriminatingreflector 42 to the beam splitter 24 is continuous and equal to the beam14 which leaves the beam splitter 24 to enter the beacon generator 28(see FIG. 6A and accompanying description). It is to be understood,however, that as beam 14 is reflected off of various surfaces and passesthrough various components of the illustrated embodiment, transmissionerrors and various inefficiencies in reflecting the beam 14 will resultin a loss in light intensity by the time it is reflected back to thebeam splitter 24.

Discriminating reflector 42 in the beacon separator 34 takes advantageof the above-mentioned loss in light intensity by reflecting a smallportion of the beacon 30 back to the beam splitter 24 before it reflectsoff of any of the other reflecting surfaces 40,44,52,70,72. Thisproduces a momentary increase in light intensity reflected back to thebeam splitter 24 to aid in discriminating between the horizontal andvertical components 36,38 of the beacon 30 reflected back to the beamsplitter 24. Other methods of discrimination may also be utilized. Forexample, a nonreflective surface could be provided in place ofdiscriminating reflector 42, which would produce an absence of reflectedlight between the horizontal and vertical components 36,38 reflectedback to the beam splitter 24. Alternatively, a series of codednonreflecting lines could be positioned near the ends of the reflectors70,72, the code telling the computer that a horizontal and/or verticalsweep has ended and/or begun. Yet another method of telling a horizontalfrom a vertical sweep would be to provide an encoder on the oscillatingmirror 32 so that the mirror's position and, therefore, the direction ofthe beam 14 is communicated to the computer.

The reflected beam 14, representatively illustrated in FIG. 1 having anunfilled arrowhead, enters the beam splitter 24 and strikes thehalf-silvered mirror 26. A portion of the reflected beam 14 is directedto a light sensor 74. A photodiode 76 in the path of the reflected beam14 is capable of measuring the beam's intensity. The photodiode 76 hasleads 78 for connecting to measurement electronics (not shown). Othermethods of measuring the beam's intensity may also be used. Use of theapparatus illustrated in FIG. 1, and the resulting measurements of theintensity of the reflected beam 14 over time, allow the position of anobject in the light grid 68 to be determined.

Turning now to FIG. 2, an embodiment of a method 150 of determining anobject's position is representatively illustrated. The method embodimentis for determining the object's position on a two-dimensional plane,although other embodiments may be used to determine the object'sposition in one or three dimensions, the object's velocity oracceleration, etc.

Commencing with step 152, a light beam is generated. The light beam iscompact and is composed of light rays which are essentially parallel toeach other. The more compact the light beam, the greater the resolutioncapability, and the more the light rays are parallel to each other, thegreater the accuracy of the method 150.

Through testing, it has been found that a conventional light emittingdiode-type infrared laser having an integral collimator produces asuitable light beam for use with the method 150. Other suitable lightbeam producers are commercially available, for example, a laser of thetype typically used in compact disk drives. It is not necessary that thelight beam produced be in the infrared range of the light spectrum.

Continuing with step 154, the beam is passed through a beam splitter.The purpose of the beam splitter in the method 150 is to separate thelight which is later reflected back to the beam splitter from the lightbeam produced in step 152. The method 150 utilizes a half-silveredmirror which passes fifty percent of the light beam, and reflects fiftypercent of the light beam. Other beam splitter configurations suitablefor use with the method 150 are commercially available, such as a dualprism having a partially-reflective film between the prisms.

In the method 150, the fifty percent of the light beam produced in step152 which is reflected by the beam splitter is not utilized. It is to beunderstood, however, that this reflected fifty percent of the light beamcould be utilized to, for example, produce a beacon as describedhereinbelow for use in determining an object's position, withoutdeviating from the principles of the present invention.

Continuing with step 156, a beacon is produced from the unreflectedfifty percent of the light beam which is passed through the beamsplitter. In the method 150, an oscillating mirror is used to reflectthe beam back and forth repeatedly, thereby producing the beacon. Theoscillating mirror is also used later in the method 150 to reflect thebeacon produced in this step back to the beam splitter.

Other beacon producing means are suitable for use in the method 150, forexample, a rotating polygonal mirror. In some respects, a rotatingmirror has advantages over the oscillating mirror. For example, arotating mirror produces a beacon which sweeps over an area repeatedlyin only one direction, instead of back and forth, making it somewhatless complex to later differentiate between the forward and backwardsweeps. Another advantage of a rotating mirror is that it typicallyproduces a linear sweep rate, that is, the beam is made to sweep over anarea with a relatively constant angular velocity, making it somewhatless complex to later compute the relationship between the beam'sposition and time. In comparison, the oscillating mirror typicallyproduces a sinusoidal sweep rate. However, the oscillating mirror isused in the embodiment method 150 because it has less bulk and fewermoving parts than a typical rotating mirror.

Continuing with step 158, the beacon produced in step 156 is separatedinto two beacon portions. Each of the beacon portions so separated isused later to determine the object's position in one dimension.Therefore, two beacon portions are needed in the method 150, since theobject's position is to be determined in two dimensions.

In the method 150, a beacon separator is utilized in step 158 which hasa reflective surface partially extending into the area swept by thebeacon produced in step 156. The reflective surface diverts a portion ofthe beacon so that it may, separately from the undiverted portion of thebeacon, be swept across the two-dimensional plane in which the object'sposition is to be determined. Other means of separating the beacon intomultiple portions, for example a prism, may also be utilized.

Continuing with step 160, the two beacon portions separated in step 158are swept over an area in which the position of the object is to bedetermined. In the method 150, the area is the two-dimensional planediscussed above. The two beacon portions are swept over the area suchthat the beacon portions are orthogonal to each other. In this manner,later computations of the object's position are somewhat less complex.It is to be understood, however, that it is not necessary for the beaconportions to be orthogonal to each other when being swept over the areain which the position of the object is to be determined.

To direct the beacon portions over the two-dimensional plane such thatthey are orthogonal to each other, each beacon portion is reflected offof a reflective surface having the property that the reflected beaconportion leaves the reflective surface at a relatively constant angleregardless the angle at which the beacon portion strikes the reflectivesurface. Thus, the angle of one beacon portion leaving one reflectivesurface may be positioned so that it is orthogonal to the other beaconportion leaving the other reflective surface.

Other means may be utilized to direct the beacon portions orthogonallyover the two-dimensional plane. For example, each beacon portion couldbe reflected off of a curved reflector having a curvature such that thebeacon portion would be reflected in the same direction no matter wherethe beacon portion strikes the curved reflector.

Continuing with step 162, after being swept over the area in which theposition of the object is to be determined, the beacon portions arereflected back to the beam splitter. The object, being positioned in thetwo-dimensional plane swept by the beacon portions, obstructs a fragmentof each beacon portion, thus preventing its reflection back to the beamsplitter.

For reflecting each beacon portion back to the beam splitter, areflective surface is utilized having the property that it reflectslight back in the same direction at which the light strikes thereflective surface. Other means, such as a mirror, may be utilized forreflecting each beacon portion back to the beam splitter.

Note that, in this step 162 of the method 150, the beacon portions arereflected back off of each reflective surface in a direction opposite tothat which they had reflected off those reflective surfaces in theprevious steps, namely, the reflective surfaces utilized to orient thebeacon portions orthogonally described in step 160 above, the reflectivesurface utilized in the beacon separator described in step 158 above(only the beacon portion diverted in step 158), and the oscillatingmirror utilized for producing the beacon as described in step 156 above.

Continuing with step 164, the beacon portions reflected back to the beamsplitter in step 162 are directed to a light sensor. The light sensormeasures the intensity of the beacon portions reflected back to the beamsplitter.

A photodiode suitable for measuring the intensity of infrared light isutilized to measure the intensity of the beacon portions reflected backto the beam splitter. Other light sensors may be used as well. It is tobe understood, however, that the light sensor must be capable ofmeasuring the intensity of the light produced in step 152 and must becapable of detecting the unreflected fragments of the beacon portions,described above in regard to step 162.

Continuing with step 166, the object's position in the two-dimensionalplane is determined. In the method 150, the unreflected fragments of thebeacon portions, detected in step 164 above, indicate the position ofthe object, since the object caused those fragments to not be reflectedback to the beam splitter in step 162 above.

One unreflected fragment will be present in each beacon portionreflected back to the beam splitter in the method 150. By computing theposition of the unreflected fragment in each beacon portion, theposition of the object in each of two dimensions can be determined.

A microprocessor is utilized to time the unreflected fragment in eachbeacon portion and compute the object's position, based on thesinusoidal sweep rate of the oscillating mirror. Since, in the method150, the beacon portions are orthogonal to each other, the object'sposition can be directly computed in Cartesian coordinates in thetwo-dimensional plane. If, however, the beacon portions are notorthogonal to each other, the object's Cartesian coordinates can stillbe computed, albeit using more complex calculations.

Turning now to FIG. 3, the optical digitizer 10 is representativelyillustrated as being disposed on a computer keyboard 80 having keys 90.The keyboard 80 is otherwise conventional, suited for input of text bytyping on keys 90, and is typically used in conjunction with a computer.

As representatively illustrated in FIG. 3, the top surface of thekeyboard 80 having the keys 90 thereon is in a vertical orientation,with the side which typically faces the user being at the bottom of theillustration. It is to be understood that, in the following description,the use of the terms "vertical" and "horizontal" refer to therepresentatively illustrated orientation of the keyboard 80 in FIG. 3.Stated in another manner, the "vertical" direction runs up and down, andthe "horizontal" direction runs side to side in FIG. 3.

Light source 12, beam splitter 24, beacon generator 28, beacon separator34, and light sensor 74 (combinatively forming the previously describedoptical digitizer 10) are shown in schematicized form, convenientlymounted near the upper left-hand portion of the keyboard 80, althoughother positionings of these elements are possible.

Reflector 44 is mounted on a support 82 to the rear of the keys 90.Reflector 72 is mounted on a support 84 to the right of the keys 90.Reflector 52 is mounted on a support 86 to the left of the keys 90.Reflector 70 is mounted on an upwardly extending and rearwardly facingportion of a space bar 88.

Points 60,62,64,66 form the corners of the rectangular light grid 68. Atthe light grid's horizontal extremities are beams 46 and 50. At thelight grid's vertical extremities are beams 54 and 56. Thus, in theillustrated embodiment, the light grid 68 is positioned over a portionof the keys 90. The light grid 68 may be enlarged or reduced to anyconvenient size or shape and may overlay all, a portion of, or none ofthe keys 90.

Illustrated in FIG. 4 is a cross-sectional view taken along line 4--4through the keyboard 80 illustrated in FIG. 3. In this view, the spacingbetween the keys 90 and the beam 50 can be seen. Reflectors 44 and 70are positioned just above the keys 90, reflector 44 being mounted tosupport 82, and reflector 70 being mounted to the space bar 88.

Positioning the optical digitizer 10 in this manner allows a computeruser to operate the digitizer 10 without removing the user's hands fromthe keyboard 80. The user can conveniently lift the fingers slightlyabove the keyboard 80, activate the optical digitizer 10 by, forexample, pressing an appropriate control or function key on thekeyboard, and then use one finger to obstruct the light grid 68 andthereby communicate positional information, select a screen object, etc.When the user is finished using the digitizer 10, it is deactivated by,for example, pressing another control or function key, and the user maytype on the keys 90 again. This is all accomplished without the user'shands leaving their normal positions above the keyboard 80.

FIG. 5 shows how the location of an obstruction 92 in the light grid 68is determined. As in the above described figures, filled arrowheadsindicate the direction of light beams which have not been reflected offof reflector 70 or 72, while blank arrowheads indicate the direction ofbeams which have been reflected off of reflector 70 or 72. Note that inFIG. 5, beams 56,50,54, and 46, and points 60,62,64, and 66 correspondto the same beams and points in FIGS. 1, 3, and 4.

Beams 46 and 50, at the outer limits of the horizontal beacon portion 48are seen to be reflected off of reflector 70. They will be detected, asdescribed above, by the light sensor 74. Likewise, beams 94 and 96,passing just to each side of the obstruction 92 are also reflected backto the light sensor 74. However, beam 98, which strikes the obstruction92 is not reflected back and, therefore, cannot be detected by the lightsensor 74. Note that each of beams 46,50,94,96, and 98 are part of thehorizontal beacon portion 48. Thus, the absence of a beam beingreflected back from the horizontal beacon portion 48 is detected by thelight sensor 74. The center of the horizontal position of theobstruction 92 can be determined by averaging the horizontal positionsof beams 94 and 96 which pass just to each side of the obstruction 92.

The vertical portion of the grid 68 operates in the same manner as thehorizontal portion. Beams 54 and 56, at the outer limits of the verticalbeacon portion 58 are seen to be reflected off of reflector 72. Theywill be detected, as described above, by the light sensor 74. Likewise,beams 100 and 102, passing just to each side of the obstruction 92 arealso reflected back to the light sensor 74. However, beam 104, whichstrikes the obstruction 92 is not reflected back and, therefore, cannotbe detected by the light sensor 74. Note that each of beams54,56,100,102, and 104 are part of the vertical beacon portion 58. Thus,the absence of a beam being reflected back from the vertical beaconportion 58 is detected by the light sensor 74. The center of thevertical position of the obstruction 92 can be determined by averagingthe vertical positions of beams 100 and 102 which pass just to each sideof the obstruction 92.

FIGS. 6A through 6E representatively illustrate how the light sensor 74receives and measures the intensity of the reflected beam 14. Thevertical scale in each of FIGS. 6A through 6E is reflected lightintensity which the photodiode 76, through leads 78, communicates to thecomputer. The horizontal scale is time. Traces on these graphs thusindicate a "snapshot" in time of the reflected light intensity "seen" bythe light sensor 74.

FIG. 6A representatively illustrates what the light sensor 74 sees whenthere is no obstruction in the light grid 68. Trace 106 is completelyflat (with the exception of small increases in intensity 108 betweenhorizontal and vertical sweeps of the beacon 30), indicating that all ofthe beam 14 from the horizontal and vertical beacon portions 48,58 isbeing reflected back off of reflectors 70 and 72.

The small increases in intensity 108 between the horizontal and verticalsweeps are due to the portion of the beacon 30 reflected back to thelight sensor 74 by the discriminating reflector 42 in the beaconseparator 34. In this manner, the computer can discriminate between avertical and a horizontal sweep. If, as described above, a nonreflectivesurface is used to discriminate between horizontal and vertical sweepsof the beacon 30, a decrease, instead of an increase 108, in lightintensity would be seen by the light sensor 74.

Note that in FIG. 6A a vertical sweep of the beacon 30 is followed byanother vertical sweep and a horizontal sweep is followed by anotherhorizontal sweep. This is due to the fact that the mirror 32 isoscillating. Each sweep is immediately repeated in reverse as the mirror32 oscillates back and forth. If a rotating polygonal mirror is usedinstead of an oscillating mirror, a vertical sweep will be followed by ahorizontal sweep and a horizontal sweep will be followed by a verticalsweep.

FIG. 6B representatively illustrates a trace 110 produced when there isan obstruction 92 in the light grid 68 near the beginning of bothhorizontal and vertical sweeps. Referring to FIG. 5, the obstruction 92would be located near point 60, but still within the light grid 68.

At the beginning of the horizontal sweep, the light intensityrepresented by trace 110 is the same as trace 106 in the previous FIG.6A. As the horizontal beacon portion 48 is reflected back to the lightsensor 74, between beams 46 and 94, the reflected light intensityremains the same (portion 112 of trace 110). Where the horizontal beaconportion 48 is not reflected back to the light sensor 74, such as beam 98between beams 94 and 96, the reflected light intensity drops (portion116 of trace 110). Between beams 96 and 50, when the horizontal beaconportion 48 is again reflected back to the light sensor 74, the reflectedlight intensity returns to its initial level (portion 114 of trace 110).An increase in light intensity 108 indicates the beginning of thevertical sweep.

As with the horizontal sweep described above, at the beginning of thevertical sweep, the light intensity represented by trace 110 is the sameas trace 106. As the vertical beacon portion 58 is reflected back to thelight sensor 74, between beams 56 and 100, the reflected light intensityremains the same (portion 118 of trace 110). Where the vertical beaconportion 58 is not reflected back to the light sensor 74, such as beam104 between beams 100 and 102, the reflected light intensity drops(portion 120 of trace 110). Between beams 102 and 54, when the verticalbeacon portion 58 is again reflected back to the light sensor 74, thereflected light intensity returns to its initial level (portion 122 oftrace 110). The remainder of trace 110 is the reverse of that describedimmediately above as the mirror 32 oscillates back to its initialposition to begin another sweep of the beacon 30.

Thus, it is seen that a drop in reflected light intensity is seen by thelight sensor 74 when an obstruction 92 is encountered in the horizontaland vertical sweeps. The center of the obstruction's position may becalculated by measuring the time from the beginning of the horizontaland vertical sweeps to the centers of the drops in reflected lightintensity (portions 116 and 120 of trace 110). The times thus measuredcorrespond to the horizontal and vertical positions of the obstruction92 in the light grid 68.

The relationship between time and horizontal and vertical positionwithin the light grid 68 will vary, depending on many factors. If, forexample, the position of the oscillating mirror 32 varies according to asinusoidal function, the relationship between time and horizontal andvertical position within the light grid 68 will also be a nonlinearfunction. If the beams which make up the horizontal or vertical beaconportion 48,58 are not parallel to each other, or if the beacon portionsare not orthogonal to each other, the relationship between time andposition will be affected accordingly.

FIG. 6C is similar to FIG. 6B, except that the representativelyillustrated portions of a trace 124 indicating a reduced reflected lightintensity 126,128 are near the end of the horizontal and verticalsweeps, respectively. Referring to FIG. 5, the trace 124 corresponds toa position of the obstruction 92 near point 66, but still within thelight grid 68. Note that, with the obstruction 92 in that position, theunreflected beam 98 in the horizontal beacon portion 48 would be nearthe end of the horizontal sweep, corresponding to portion 126 of trace124, and that the unreflected beam 104 in the vertical beacon portion 58would be near the end of the vertical sweep, corresponding to portion128 of trace 124.

Representatively illustrated in FIG. 6D are portions of a trace 130having reduced reflected light intensity 132,134 near the beginning ofthe horizontal sweep and near the end of the vertical sweep of thebeacon 30. This corresponds to a position of the obstruction 92 nearpoint 64, but still within the light grid 68 (see FIG. 5).

Representatively illustrated in FIG. 6E are portions of a trace 136having reduced reflected light intensity 138,140 near the end of thehorizontal sweep and near the beginning of the vertical sweep of thebeacon 30. This corresponds to a position of the obstruction 92 nearpoint 62, but still within the light grid 68 (see FIG. 5).

Thus, a person of ordinary skill in the art, given the characteristicsof the optical digitizer 10 and the reflected light intensity detectedover time by the light sensor 74, is able to determine the position ofan obstruction 92 anywhere within the light grid 68.

Up to this point, the optical digitizer 10 has been described withoutregard to the relationship between a plane across which the horizontalbeacon portion 48 is swept and a plane across which the vertical beacon58 portion is swept. FIGS. 1, 3, and 5 illustrate embodiments in whichthe above described planes are coplanar. If, however, the planes are notcoplanar, the optical digitizer 10 functions as described hereinabove,but the obstruction 92 is then permitted to obstruct one of the beaconportions 48,58 without obstructing the other. It is then possible toperform other functions, for example, measure the velocity of theobstruction 92 by dividing the distance separating the planes swept bythe horizontal and vertical beacon portions 48,58 by the difference intime between when the light sensor 74 sees a reduced reflected lightintensity in each sweep.

It is also possible to determine the position of an obstruction in moreor less than two dimensions using the principles of the presentinvention. If only one spatial dimension is desired, then only onebeacon portion is needed. If three spatial dimensions are desired, morethan one optical digitizer 10 may be stacked to form a three-dimensionallight grid.

Illustrated in FIG. 7 is another embodiment of an optical digitizer 200.It is shown in highly schematicized form for the purpose of clarity.Dashed lines and arrows are used to represent paths and directions,respectively, of light. Filled arrowheads represent directions ofunreflected light and unfilled arrowheads represent directions ofreflected light in a manner similar to that used in FIGS. 1, 3, 4, and5. In the optical digitizer 200 illustrated in FIG. 7, however, light isreflected in more than one plane.

A light source 202 provides a compact beam of light 204 which is in theinfrared portion of the light spectrum in the illustrated embodiment.The light source 202 includes a laser 206 which, in turn, includes alight emitting diode 208 and a collimator 210. The light emitting diode208 produces infrared light. The infrared light produced by the lightemitting diode 208 is made into the beam 204 having essentially parallelsides by the collimator 210.

The beam 204 next passes through a half-silvered mirror 212 which passeshalf of the beam 204 and reflects the other half. The reflected half ofthe beam 204 is not used in the illustrated embodiment, so it is notshown in FIG. 7. The half-silvered mirror 212 performs essentially thesame function in the optical digitizer 200 representatively illustratedin FIG. 7 as the half-silvered mirror 26 in the beam splitter 24illustrated in FIG. 1.

The beam 204 next passes through a refracting surface 214 and into asubstantially transparent and planar lightguide 215. The lightguide 215has a refractive index different than that of air, such that the beam204 changes direction as it passes through the refracting surface 214.The material of which the lightguide 215 is constructed is clearplastic, although other materials, for example, glass, may be used. Thepurpose of the refracting surface 214 in the illustrated opticaldigitizer 200 is to enhance packaging, i.e., to permit the light source202, half-silvered mirror 212, etc., to be positioned for optimumcompactness.

The beam 204 next passes through the lightguide 215 to an oscillatingmirror 216. The beam 204 reflects off of the oscillating mirror 216,producing a beacon 218. The beacon 218 differs from the beam 204 in thatthe beacon 218 "sweeps" across a plane, whereas the beam 204 remainsstationary. In other words, the beacon 218 is the beam 204 put intomotion by the oscillating mirror 216.

It is to be understood that the beacon 218 may be generated from thebeam 204 by other methods as well. For example, instead of theoscillating mirror 216, a rotating polygonal mirror could be used torepeatedly and sequentially sweep beam 204 across an area. As a furtherexample, beam 204 could be directed across a curved surface instead of aflat plane.

The beacon 218 is directed by the oscillating mirror 216 to sweep acrosstwo parabolic mirrors formed on edges of the lightguide 215, one ofwhich 220 is oriented generally vertical as viewed in FIG. 7, and theother of which 222 is oriented generally horizontal as viewed in FIG. 7.A portion of the beacon 218, the "vertical" component 224 sweeps acrossthe vertical parabolic mirror 220. Likewise, a "horizontal" beaconcomponent 226 sweeps across the horizontal parabolic mirror 222. In amanner that will be readily appreciated by one of ordinary skill in theart, and which is described more fully hereinbelow, the horizontalcomponent 226 and horizontal parabolic mirror 222 are utilized todetermine an object's horizontal position within a light grid, and thevertical component 224 and vertical parabolic mirror 220 are utilized todetermine the object's vertical position within the light grid.

The horizontal parabolic mirror 222 in the illustrated optical digitizer200 has a smooth upwardly facing surface 234 with reflective material235, such as silver, applied thereto. The upwardly facing surface 234has a parabolic shape so that the radially-directed horizontal component226, once reflected off of the upwardly facing surface 234 will sweephorizontally as a beacon having parallel sides. The vertical parabolicmirror is similarly constructed so that the radially directed verticalcomponent 224, once reflected off of leftwardly facing surface 236, willsweep vertically as a beacon having parallel sides.

When the horizontal component 226 reflects off of the horizontalparabolic mirror 222, it is directed in an upward direction as viewed inFIG. 7. Thus, it can be seen that as the horizontal component 226 of thebeacon 218 sweeps across the upwardly facing surface 234 of horizontalparabolic mirror 222, it is made to sweep horizontally from side to sideas viewed in FIG. 7. The lowermost limit of the horizontal component226, illustrated as a beam 228, once reflected off of the horizontalparabolic mirror 222, becomes the leftmost limit of a horizontal beaconportion 230 as viewed in FIG. 7. The uppermost limit of the horizontalcomponent 226, illustrated as a beam 232, once reflected off of thehorizontal parabolic mirror 222, becomes the rightmost limit of thehorizontal beacon portion 230 as viewed in FIG. 7. Therefore, thehorizontal beacon portion 230 is nothing more than the horizontalcomponent 226 of the beacon 218 reflected off of the horizontalparabolic mirror 222.

In FIG. 7, it can be seen that beam 228 strikes the horizontal parabolicmirror 222 at a slightly different angle than does beam 232, however,once reflected off of horizontal parabolic mirror 222, beams 228 and 232are parallel in the horizontal beacon portion 230. It is to beunderstood that, in carrying out the principles of the presentinvention, the horizontal parabolic mirror 222 does not have to be anintegral portion of lightguide 215 or be silver-coated, and that beams228 and 232 do not have to be parallel in the horizontal beacon portion230. The horizontal parabolic mirror 222 could have a shape other thanparabolic.

Vertical component 224 of the beacon 218, after reflecting off theoscillating mirror 216, strikes the vertical parabolic mirror 220 whichis constructed in a manner similar to the horizontal parabolic mirror222 in the illustrated embodiment. A beam 238, lowermost in the verticalcomponent 224 as illustrated in FIG. 7, strikes the vertical parabolicmirror 220 and is reflected to the left in a direction orthogonal to thehorizontal beacon portion 230. A beam 240, uppermost in the verticalcomponent 224, strikes the vertical parabolic mirror 220 and is alsodirected to the left, orthogonal to horizontal beacon portion 230 asillustrated in FIG. 7. Thus, it can be seen that vertical component 224of the beacon 218 is reflected off of vertical parabolic mirror 220 sothat it sweeps vertically, as illustrated in FIG. 7, between therepresentatively shown beams 238 and 240, forming a vertical beaconportion 242 which is orthogonal to horizontal beacon portion 230. Notethat, as with horizontal parabolic mirror 222 described above, verticalparabolic mirror 220 could have a different shape and could be made ofother materials.

Since beam 204 is continuously directed to the oscillating mirror 216,the resulting beacon 218 is also continuous. Therefore, although beams228 and 232 are illustrated as being at the outer limits of horizontalbeacon portion 230, and beams 238 and 240 are illustrated as being atthe outer limits of vertical beacon portion 242, it is important tounderstand that the beam 204, in the form of the vertical or horizontalbeacon portion 230,242 sweeps continuously between these outer limits.Note, however, that at any one instant in the illustrated embodiment,beam 204 may be directed to the horizontal beacon portion 230 orvertical beacon portion 242, but not both.

It is also important to note at this point that although separate beams228,232,238,240 are referred to in this description of the illustratedembodiment, no two of these are present at one time, since they allemanate from the same beam 204 produced by the light source 202. Beams228,232,238,240 representatively illustrated in FIG. 7 are all simplydifferent positions of beam 204. Likewise, different beacon portions230,242 and beacon components 224,226 are just parts of beacon 218,which is, in turn, made up of different positions of beam 204 producedby the oscillating mirror 216.

Beam 240 intersects beam 228 at point 244 and intersects beam 232 atpoint 246. Beam 238 intersects beam 228 at point 248 and intersects beam232 at point 250. Since the horizontal beacon portion 230 is orthogonalto the vertical beacon portion 242, points 244, 246, 248, and 250 definethe corners of a rectangular light grid 252. In this light grid 252, thehorizontal beacon portion 230 sweeps from side to side, and the verticalbeacon portion 242 sweeps from top to bottom, as representativelyillustrated in FIG. 7. For the purpose of further description of theillustrated embodiment, the defined beginning of the sweep of thehorizontal beacon portion 230 shall be at its leftmost limit (beam 228as illustrated in FIG. 7), and the defined beginning of the sweep of thevertical beacon portion 242 shall be at its lower limit (beam 238 asillustrated in FIG. 7).

It is to be understood that the light grid 252 could have a shape otherthan rectangular. If, as described above, beams 228 and 232 are notparallel to each other, a trapezoid shape is produced. If, additionally,beams 240 and 238 are not parallel to each other, another polygonalshape is produced. Light grid 252 may take virtually any shape as longas no beam in the horizontal beacon portion 230 is collinear with a beamin the vertical beacon portion 242.

In a unique manner more fully described hereinbelow, the horizontal andvertical beacon portions 230 and 242, and the light grid 252 definedthereby, are "transposed", that is, transferred to another plane,different from a plane in which the components of the optical digitizer200 heretofore described lie. Thus, the light source 202, half-silveredmirror 212, lightguide 215, oscillating mirror 216, horizontal parabolicmirror 222, and vertical parabolic mirror 220 all lie in a plane asrepresentatively illustrated in FIG. 7. The light beam 204 and some ofits permutations (vertical portion 242, horizontal portion 230, andlight grid 252), however, coexist on another, transposed, plane.

This transposition is accomplished by means of two light pipes, avertical light pipe 254 which transposes the vertical beacon portion242, and which is generally vertically oriented as shown in FIG. 7, anda horizontal light pipe 256 which transposes the horizontal beaconportion 230, and which is generally horizontally oriented as shown inFIG. 7. Vertical light pipe 254 takes the leftwardly directed verticalbeacon portion 242, transposes it, and directs it to the right as viewedin FIG. 7. Horizontal light pipe 256 takes the upwardly directedhorizontal beacon portion 230, transposes it, and directs it downward asviewed in FIG. 7. Light pipes 254 and 256 are described more fully belowin the detailed description accompanying FIG. 8.

After the horizontal beacon portion 230 has been transposed and directeddownward by the horizontal light pipe 256, as described above, reflector258, representatively illustrated in FIG. 7 as being horizontallydisposed at the lowermost extent of horizontal beacon portion 230,reflects the horizontal beacon portion 230 directly back in thedirection of horizontal light pipe 256 and thence downwardly back tohorizontal parabolic mirror 222. Unfilled arrowheads on beamsrepresentatively illustrated in horizontal beacon portion 230 indicatethe direction of beams which have reflected off of reflector 258. Thus,beams in the horizontal beacon portion 230 are reflected from thehorizontal light pipe 256 back through the lightguide 215 to horizontalparabolic mirror 222, through the lightguide 215 again to theoscillating mirror 216, through the lightguide 215 yet again, and thenceto the half-silvered mirror 212.

In a similar manner, reflector 260, representatively illustrated in FIG.7 as being vertically disposed at the right-hand edge of vertical beaconportion 242, reflects the vertical beacon portion 242 directly back inthe direction of vertical light pipe 254, through the lightguide 215,and thence back to vertical parabolic mirror 220. Unfilled arrowheads onbeams representatively illustrated in vertical beacon portion 242indicate the direction of beams which have reflected off of reflector260. Thus, beams in the vertical beacon portion 242 are reflected backthrough the lightguide 215 to vertical parabolic mirror 220, through thelightguide 215 again to the oscillating mirror 216, through thelightguide 215 yet again, and thence to the half-silvered mirror 212.

Reflectors 258 and 260, in the illustrated embodiment, are made of amaterial which reflects light back in the same direction at which itinitially strikes the material. It is known to those skilled in the artas retro-reflecting film. There are several types of retro-reflectingfilm, including micro corner cube and micro sphere. The micro cornercube type has been found to give acceptable results in the illustratedembodiment apparatus.

In the illustrated embodiment, with no obstruction blocking the path ofany beam, the cumulative total of the beams reflected back from thehorizontal and vertical beacon portions 230,242 is continuous and equalto the beam 204 which leaves the half-silvered mirror 212, with theexception of the portion which strikes the refractive surface 214between the horizontal and vertical parabolic mirrors 220,222. Thus,referring to FIGS. 6A-6E, the increased reflected light intensityportion 108 between successive vertical and horizontal sweeps,corresponds to that portion of beacon 218 which is directed back throughthe refractive surface 214 between beacon portions 224 and 226. It is tobe understood, however, that as beam 204 is reflected off of varioussurfaces and passes through various components of the illustratedembodiment, transmission errors and various inefficiencies in reflectingthe beam 204 will result in a loss in light intensity by the time it isreflected back to the half-silvered mirror 212. As with the previouslydescribed and illustrated optical digitizer 10, other methods ofdiscriminating between horizontal and vertical sweeps may be utilized aswell.

The reflected beam 204, representatively illustrated in FIG. 7 having anunfilled arrowhead, is reflected back off of the oscillating mirror 216,back through the lightguide 215, and strikes the half-silvered mirror212. A portion of the reflected beam 204 is directed to a photodiode 262in the path of the reflected beam 204, which is capable of measuring thebeam's intensity. Other methods of measuring the beam's intensity mayalso be used. Use of the apparatus illustrated in FIG. 7, and theresulting measurements of the intensity of the reflected beam 204 overtime (see FIGS. 6A-6E), allow the position of an object in the lightgrid 252 to be determined as described hereinabove.

Turning now to FIG. 8, a cross-sectional view of the optical digitizer200 representatively illustrated in FIG. 7 is shown. For the purpose ofclarity, only one representative beam 240 is shown in this view. Thepath of this beam 240 will be described below so that a completeunderstanding may be had of the manner in which the light grid 252 (seeFIG. 7) is vertically transposed.

Beam 240 originates at the oscillating mirror 216 when beam 204 (seeFIG. 7) strikes the oscillating mirror 216 while it is directed towardthe vertical parabolic mirror 220. At this point, beam 240 is a portionof the vertical beacon component 224 (see FIG. 7). Beam 240 leaves theoscillating mirror 216, travels through the lightguide 215, strikes thevertical parabolic mirror 220, and is reflected back through thelightguide 215. At this point, beam 240 is a portion of the verticalbeacon portion 242 (see FIG. 7).

After being reflected off of the vertical parabolic mirror 220 andtraveling through lightguide 215, beam 240 enters the vertical lightpipe 254. The beam 240 first strikes and is reflected off of a rightangle reflector 264. The right angle reflector 264 directs the beam 240vertically upward as viewed in FIG. 8. Right angle reflector 264 may beconstructed of any suitable material, such as a conventional mirror,capable of reflecting the beam 240. The material of which the rightangle reflector 264 is made is silver-coated clear plastic.

Beam 240 travels upwardly after being reflected off of the right anglereflector 264 and strikes a reflector 266. Reflector 266 directs thebeam 240 horizontally to the right as viewed in FIG. 8. Reflector 266 isconstructed using a material commonly known to those skilled in the artas right-angle film. Right-angle film reflects light back at a ninetydegree included angle and is available from the 3M Corporation.

Beam 240 leaves reflector 266 and travels to the right as viewed in FIG.8, and passes in front of the horizontal light pipe 256, which isconstructed in a manner similar to the vertical light pipe 254 describedabove. As also described above, the horizontal beacon portion 230 (seeFIG. 7) is transposed and, as representatively illustrated, intersectsthe vertically transposed vertical beacon portion 242 (see FIG. 7).

As beam 240 passes in front of the horizontal light pipe 256, itintersects beam 228 (see FIG. 7) at point 244, at a corner of the lightgrid 252 (see FIG. 7). Likewise, beam 240 intersects beam 232 (see FIG.7) at point 246, at another corner of the light grid 252. The beam 240continues traveling to the right until it strikes vertical reflector260.

Beam 240 reflects off of reflector 260 and is directed horizontally tothe left as viewed in FIG. 8. From this point, unless interrupted by anobject in its path, beam 240 retraces its path and is verticallytransposed back down into the lightguide 215 by the vertical light pipe254. Unfilled arrowheads indicate the direction of the beam 240 after ithas been reflected off of reflector 260.

After being reflected back into the lightguide 215, the beam 240reflects off the vertical parabolic mirror 220 and is directed backthrough the lightguide 215 to the oscillating mirror 216, and thenceback through the light guide 215, the refracting surface 214 (see FIG.7), and to the half-silvered mirror 212 as described above.

Shown in FIG. 9 is a partially cut away keyboard 280. The keyboard 280takes advantage of the vertical transposition of the light grid 252 bythe optical digitizer 200 described above, to position the light grid252 above keys 282 disposed on the keyboard 280.

Keyboard 280 has a housing 284 which supports a keypad 286. The keys 282are distributed about the keypad 286 and include a space bar 288.Beneath the keypad 286, components of the optical digitizer 200 (morecompletely described hereinabove and representatively illustrated inFIGS. 7 and 8), including the light source 202, half-silvered mirror212, photodiode 262, lightguide 215, horizontal and vertical parabolicmirrors 222,220, and oscillating mirror 216, are contained within thekeyboard housing 284.

Horizontal and vertical light pipes 256 and 254 vertically transpose thelight grid 252 so that it is disposed above the keys 282. In thismanner, a user may utilize a finger or other object to interrupt thelight grid 252 above the keys 282 in order to indicate a position on acomputer screen as more fully described hereinabove. It is to beunderstood that the light grid 252 may also be otherwise utilized inapparatus other than a keyboard.

Horizontal reflector 258 is attached to the space bar 288, facing thehorizontal light pipe 256, similar to the manner in which reflector 70is attached to space bar 88 in optical digitizer 10 representativelyillustrated in FIG. 3. Horizontal and vertical light pipes 256 and 254extend through the keypad 286 so that the light grid 252 is verticallytransposed above the keys 282. In this configuration, referring also toFIG. 8, the keypad 286 is disposed vertically between the right anglereflector 264 and reflector 266 of the vertical light pipe 254.

It is to be understood that the light pipes 254 and 256 may be otherwiseconstructed and mounted to the keypad 256. For example, the light pipesmay be constructed so that they telescope into and out of the keypad256. In this manner, the keyboard 280 may be made to more compactly nestagainst a computer screen for compact storage.

Illustrated in FIG. 10 is another embodiment of an optical digitizer300. It is shown in highly schematicized form for the purpose ofclarity. Dashed lines and arrows are used to represent paths anddirections, respectively, of light. Filled arrowheads representdirections of light in one plane and unfilled arrowheads representdirections of light that has been transposed to another plane in amanner that will become clear upon consideration of the detaileddescription hereinbelow.

In the optical digitizer 300 illustrated in FIG. 10, similar to theoptical digitizer 200 illustrated in FIG. 7, light is reflected in morethan one plane. Elements of the optical digitizer 300 representativelyillustrated in FIG. 10, which have substantially the same function andstructure as elements representatively illustrated in FIG. 7, have beenidentified in FIG. 10 with the same item numbers, and are not furtherdescribed hereinbelow, unless such further description is helpful tofully and completely describe the optical digitizer 300.

A light source 202 provides a compact beam of light 204 which is in theinfrared portion of the light spectrum. The beam 204 next passes througha refracting surface 214 and into substantially transparent lightguide215. Note that optical digitizer 300 as representatively illustrateddoes not include a beam splitter or half-silvered mirror. The beam 204next passes to an oscillating mirror 216. The beam 204 reflects off ofthe oscillating mirror 216, producing a beacon 218.

The beacon 218 is directed by the oscillating mirror 216 to sweep acrosstwo parabolic mirrors, one of which 220 is oriented generally verticalas viewed in FIG. 10, and the other of which 222 is oriented generallyhorizontal as viewed in FIG. 10. A portion of the beacon 218, the"vertical" component 224 sweeps across the vertical parabolic mirror220. Likewise, a "horizontal" beacon component 226 sweeps across thehorizontal parabolic mirror 222.

When the horizontal component 226 reflects off of the horizontalparabolic mirror 222, it is directed in an upward direction as viewed inFIG. 10. The lowermost limit of the horizontal component 226,illustrated as a beam 228, once reflected off of the horizontalparabolic mirror 222, becomes the leftmost limit of a horizontal beaconportion 230 as viewed in FIG. 10. The uppermost limit of the horizontalcomponent 226, illustrated as a beam 232, once reflected off of thehorizontal parabolic mirror 222, becomes the rightmost limit of thehorizontal beacon portion 230 as viewed in FIG. 10.

Vertical component 224 of the beacon 218, after reflecting off of theoscillating mirror 216, strikes the vertical parabolic mirror 220 whichis constructed in a manner similar to the horizontal parabolic mirror222 in the illustrated embodiment. A beam 238, lowermost in the verticalcomponent 224 as illustrated in FIG. 10, strikes the vertical parabolicmirror 220 and is reflected to the left in a direction orthogonal to thehorizontal beacon portion 230. A beam 240, uppermost in the verticalcomponent 224, strikes the vertical parabolic mirror 220 and is alsodirected to the left, orthogonal to horizontal beacon portion 230 asillustrated in FIG. 10. Thus, it can be seen that vertical component 224of the beacon 218 is reflected off of vertical parabolic mirror 220 sothat it sweeps vertically, as illustrated in FIG. 10, between therepresentatively shown beams 238 and 240, forming a vertical beaconportion 242 which is orthogonal to horizontal beacon portion 230.

Beam 240 intersects beam 228 at point 244 and intersects beam 232 atpoint 246. Beam 238 intersects beam 228 at point 248 and intersects beam232 at point 250. Since the horizontal beacon portion 230 is orthogonalto the vertical beacon portion 242, points 244, 246, 248, and 250 definethe corners of a rectangular light grid 252. In this light grid 252, thehorizontal beacon portion 230 sweeps from side to side, and the verticalbeacon portion 242 sweeps from top to bottom, as representativelyillustrated in FIG. 10.

In a unique manner more fully described hereinbelow, the horizontal andvertical beacon portions 230 and 242, and the light grid 252 definedthereby are transferred to another plane, different from a plane inwhich the components of the optical digitizer 300 heretofore describedlie. Thus, the light source 202, lightguide 215, oscillating mirror 216,horizontal parabolic mirror 222, and vertical parabolic mirror 220 alllie in a plane as representatively illustrated in FIG. 10. The lightbeam 204 and some of its permutations (vertical portion 242, horizontalportion 230, and light grid 252), however, coexist on another,transposed, plane.

This transposition is accomplished by means of two light pipes, avertical light pipe 254 which vertically transposes the vertical beaconportion 242 and is generally vertically oriented as shown in FIG. 10,and a horizontal light pipe 256 which vertically transposes thehorizontal beacon portion 230 and is generally horizontally oriented asshown in FIG. 10. Vertical light pipe 254 takes the leftwardly directedvertical beacon portion 242, transposes it, and directs it to the rightas viewed in FIG. 10. Horizontal light pipe 256 takes the upwardlydirected horizontal beacon portion 230, transposes it, and directs itdownward as viewed in FIG. 10. Light pipes 254 and 256 are describedmore fully above in the detailed description accompanying FIG. 8.Directions of beams which have been transposed are indicated in FIG. 10with unfilled arrowheads.

After the horizontal beacon portion 230 has been transposed and directeddownward by the horizontal light pipe 256, as described above, aconventional linear detector 302, representatively illustrated in FIG.10 as being horizontally disposed at the lowermost extent of horizontalbeacon portion 230, senses light intensity along its length. The lineardetector 302 is of the type that is capable of indicating the lightintensity of a beam which strikes anywhere on its upwardly facing (asviewed in FIG. 10) surface 306. In a similar manner, conventional lineardetector 304, representatively illustrated in FIG. 10 as beingvertically disposed at the right-hand edge of vertical beacon portion242, senses the light intensity along its length of the beam 204 in thevertical beacon portion 242.

Plotting the light intensity over time as sensed by the horizontal andvertical linear detectors 302,304 will yield plots which aresubstantially the same as those representatively illustrated in FIGS.6A-6E, with the exception that the vertical and horizontal sweeps willbe separated, because they are sensed by separate linear detectors302,304, and there will be no increase in light intensity 108 betweenthe horizontal and vertical sweeps. Note that there is no need todiscriminate between horizontal and vertical sweeps since these aresensed by separate detectors 302,304.

Other methods of measuring the beam's horizontal and vertical positionmay also be used. Use of the apparatus 300 illustrated in FIG. 10, andthe resulting measurements of the intensity of the beam 204 over time(see FIGS. 6A-6E), allow the position of an object in the light grid 252to be determined as described hereinabove.

It will be readily apparent to one of ordinary skill in the art that thelight grid 252 of the optical digitizer 300 representatively illustratedin FIG. 10 may be disposed overlying a keyboard, and the light source202, lightguide 215, oscillating mirror 216, and horizontal and verticalparabolic mirrors 222 and 220 may be disposed beneath the keyboard aswith the optical digitizer 200 representatively illustrated in FIG. 9.If such an arrangement is desired, horizontal linear detector 302 can besubstituted for the reflector 258 on the space bar, and vertical lineardetector 304 can be substituted for the reflector 260 to the right ofthe keys as representatively illustrated in FIG. 9.

Shown in FIG. 11 is a keyboard 310. The keyboard 310 takes advantage ofthe vertical transposition of the light grid 252 by the opticaldigitizer 300 described above, to position the light grid 252 above keys282 disposed on the keyboard 310, in a manner similar to the keyboard280 representatively illustrated in FIG. 9. In the keyboard 310illustrated in FIG. 11, however, the optical digitizer 300 issubstituted for the optical digitizer 200. Elements of keyboard 310 thatare substantially similar in function and structure are identified withthe same item numbers in FIG. 11 as in FIG. 9.

Keyboard 310 has a housing 284 which supports a keypad 286. The keys 282are distributed about the keypad 286 and include a space bar 288.Beneath the keypad 286, components of the optical digitizer 300 (morecompletely described hereinabove and representatively illustrated inFIG. 10), including the light source 202, lightguide 215, horizontal andvertical parabolic mirrors 222, 220, and oscillating mirror 216, arecontained within the keyboard housing 284.

Horizontal and vertical light pipes 256 and 254 vertically transpose thelight grid 252 so that it is disposed above the keys 282. In thismanner, a user may utilize a finger or other object to interrupt thelight grid 252 above the keys 282 in order to indicate a position on acomputer screen as more fully described hereinabove. It is to beunderstood that the light grid 252 may be utilized in an apparatus otherthan a keyboard 310.

Horizontal linear detector 302 is attached to the space bar 288, facingthe horizontal light pipe 256, similar to the manner in which horizontalreflector 258 is attached to space bar 288 in optical digitizer 200representatively illustrated in FIG. 9. Horizontal and vertical lightpipes 256 and 254 extend through the keypad 286 so that the light grid252 is vertically transposed above the keys 282.

It is to be understood that the light grid 252 may be positionedrelative to other structures, such as a flat planar surface or a curvedsurface. It is also to be understood that light grid 252 may be in morethan one plane above the keypad 286, the vertical and horizontal beaconportions 230 and 242 (see FIG. 10) being vertically transposed by thelight pipes 254 and 256 to different planes above the keypad 286,enabling the velocity of an object obstructing the transposed beaconportions 230 and 242 to be calculated as more fully describedhereinabove.

Referring additionally now to FIG. 12, a computer system 410 embodyingprinciples of the present invention is representatively illustrated. Thecomputer system 410 is shown in highly schematicized form forillustrative clarity. Included in the computer system 410 are a monitor412, a central processing unit (CPU) 414 interconnected to the monitor412, and an apparatus, representatively a keyboard 416, interconnectedto the CPU. As will be more fully described hereinbelow, the keyboard416 includes features which uniquely permit the position of an object418, such as a finger, stylus, pencil, etc., to be determined andcommunicated to the CPU.

For determining the object's position, the keyboard 416 includes anoptical digitizer 420 disposed thereon. The optical digitizer 420includes several elements which are representatively illustrated in FIG.12 as discreet components mounted to an upper surface of the keyboard416. However, it is to be clearly understood that one or more of theelements of the optical digitizer 420 may be mounted below the keyboard416 upper surface, for example, in a manner similar to the manner inwhich portions of the optical digitizer 300 are mounted as shown in FIG.11, and that one or more of the elements may be compactly packaged, forexample, so that they are not distributed across large areas of thekeyboard, without departing from the principles of the presentinvention.

In the optical digitizer 420 representatively illustrated in FIG. 12,the object 418 reflects back a portion of each of two beacons to a pairof corresponding light sensors, these reflections are sensed by thesensors, and the object's position is determined by conventionaltriangulation techniques. Thus, the optical digitizer 420 differs in onerespect from the other optical digitizers described hereinabove in thatthe object 418 is utilized to reflect light back to one or more sensors,instead of being utilized to obstruct reflections of light back to oneor more sensors. Of course, it will be readily appreciated by one ofordinary skill in the art that an object obstructing one or more of thelight beacons in the previously described optical digitizers will infact reflect some light (albeit at a diminished intensity asrepresentatively illustrated in FIGS. 6B-6E) back to one or more of thesensors.

In FIG. 12, dashed lines and arrows are used to represent paths anddirections, respectively, of light. Filled arrowheads representdirections of light beams which have not yet been reflected off of theobject 418, and unfilled arrowheads represent directions of light beamswhich have been reflected off of the object.

The optical digitizer 420 includes two beacon-producing andlight-sensing modules 422, 424, each of which is made up of similarelements. Therefore, only one of the modules 422, 424 will be describedherein. However, it is to be clearly understood that it is not necessaryfor the modules 422, 424 to be similarly configured, or for the modulesto include similar elements, in the optical digitizer 420.

The module 422 includes a light source 426 for producing a compact beamof light 428. The light beam 428 is in the infrared portion of the lightspectrum, but it is to be understood that the light beam may have otherwavelengths without departing from the principles of the presentinvention. The light source 426 includes a laser 430 which, in turn,includes a light emitting diode 432 and a collimator 434. The lightemitting diode 432 produces infrared light, which is made into the beam428 having essentially parallel sides by the collimator 434. As analternative, a conventional non-coherent light emitting diode (notshown) or other light source could be used in place of the laser 430.

The beam 428 next passes into a beam splitter 436. The beam splitter 436includes a half-silvered mirror 438, which passes half of the beam 428and reflects the other half. The reflected half of the beam 428 is notused in the module 422, so it is not shown in FIG. 12. However, in analternate embodiment of the present invention, the reflected half of thebeam 428 may be utilized in the other module 424, so that another lightsource 426 is not needed.

The beam 428 next passes into a beacon generator 440. The beacongenerator 440 produces a beacon 444 from the beam 428 by reflecting thebeam off of an oscillating mirror 442. For illustrative clarity, onlyone portion of the beacon 444 is representatively illustrated in FIG. 12(specifically, that portion of the beacon which strikes the object 418),but it is to be understood that the beacon actually sweeps across aplane above the upper surface of the keyboard 416. Thus, the beacon 444is the beam 428 put into motion by the oscillating mirror 442.

Of course, the beacon 444 may be generated from the beam 428 by anothermethod without departing from the principles of the present invention.For example, a rotating polygonal mirror could be used to repeatedly andsequentially sweep the beam 428 across another plane or curved surface.

In a similar manner, the module 424 includes another light source 426which produces a light beam 446. The light beam 446 is put into motionby another beacon generator 440, thereby producing another beacon 448.The beacon 448 sweeps across a plane above the upper surface of thekeyboard 416. One portion of the beacon 448 is representativelyillustrated in FIG. 12 striking the object 418.

It will be readily appreciated by one of ordinary skill in the art thatthe beacons 444, 448 sweep across intersecting or overlaid areas abovethe keyboard 416. These areas where both beacons 444, 448 sweep acrossthe keyboard 416 form a light grid 450. The grid 450 may have anydesired shape, depending upon the placement of the modules 422, 424 withrespect to the keyboard 416, and with respect to each other. Forexample, both beacons 444, 448 may sweep above substantially all of theupper surface of the keyboard 416, in which case the light grid 450would encompass substantially all of the upper surface of the keyboard.Alternatively, the beacons 444, 448 may only intersect or both overlayonly a small area above the keyboard 416 upper surface.

Additionally, although the modules 422, 424 are representativelyillustrated having their respective mirrors 442 positioned at upper leftand upper right hand corners, respectively, of the keyboard 416 uppersurface as viewed in FIG. 12, it is to be clearly understood that themodules and mirrors may be otherwise positioned without departing fromthe principles of the present invention. It will be readily appreciatedby one of ordinary skill in the art that the shape of the light grid 450may be conveniently changed by repositioning the modules 422, 424.However, for ease of calculating the object's 418 position, the modules422, 424 preferably are not positioned so that the beacons 444, 448 arecollinear at any time.

In order to calculate the position of the object 418, the beacons 444,448 are reflected by the object back to the mirrors 442, thence to themirrors 438, and thence to respective light sensors 452. The lightsensors 452 detect the reflected beacons 444, 448 and, the positions andangular orientations of the respective mirrors 442 being known at thetime the reflected beacons are detected, conventional triangulationtechniques well known to those of ordinary skill in the art may beutilized to determine the position of the object 418. For example, ifthe beacon generators 440 include oscillating mirrors 442 havingsinusoidal sweep rates, the sinusoidal function may be utilized todetermine the angular positions of the respective mirrors 442 at thetime the reflected beacons 444, 448 are detected by the respectivesensors 452. As another example, if the beacon generators 440 includerotating mirrors having linear sweep rates, a linear function may beutilized to determine the angular positions of the respective mirrors.

In one embodiment of the present invention, the light sensors 452 mayeach include a photodiode which senses light intensity, and which isuseful in the optical digitizer 420 for detecting the presence orabsence of light reflected off of the object 418. In another embodimentof the present invention, each of the light sensors 452 may include adetector 454 known to those skilled in the art as an imaging detector,that is, a detector that responds to reception of light in twodimensions, typically by utilizing an array of photosensitive cells,such as a charge coupled device. Where imaging detectors 454 are used inthe light sensors 452, the CPU 414 may be programmed with conventionalimage recognition software, so that the presence of the object 418 isdetected when the image of the object is received by the detectors andthat image matches the desired image, as determined by the imagerecognition program.

Referring additionally now to FIG. 13, a method by which the opticaldigitizer 420 may be modified to enhance its use is representativelyillustrated. In FIG. 13, one of the oscillating mirrors 442 is showndirecting the beacon 444 toward the object 418, which isrepresentatively shown as a finger. The mirror 442 and object 418 areshown apart from the keyboard 416 and remainder of the optical digitizer420 of FIG. 12 for illustrative clarity, and it is to be clearlyunderstood that, although only one of the beacons 444, 448 and one ofthe oscillating mirrors 442 is shown in FIG. 13, that the modificationsshown in FIG. 13 may also be applied to the other one of each in theoptical digitizer.

In FIG. 13, the beacon 444 is modified by passing it through a lens 456before the beacon strikes the object 418. The lens 456 is an elongatedaspherical cylindrical lens which permits a horizontal "slice" 458 ofthe beacon 444 reflected off of the object 418 to be directed back tothe mirror 442 and thence to the light sensor 452. In this manner, thelight sensor 452 only "sees" the horizontal slice 458 of the reflectedbeacon 444, thereby limiting the amount of extraneous light received bythe light sensor 452. Although in FIG. 13 the slice 458 is shownsomewhat elevated in its intersection with the object 418, it is to beunderstood that this is merely illustrative, that the slice 458 mayactually intersect the object at or near a lower tip 474 thereof, andthat the width of the slice may be increased or decreased as desired.

It will be readily appreciated by one of ordinary skill in the art thatother lenses, and other positionings of lenses, may be utilized torestrict the width, height, etc. of the beacons 444, 448 received by thelight sensors 452. For example, a lens similar to, or differentlyconfigured as compared to, the lens 456 may be placed in the path of thereflected beacon 444 between the mirror 442 and the mirror 438, betweenthe mirror 438 and the light sensor 452, etc.

To limit the amount of the beacon 444 inadvertently reflected back tothe mirror 442, one or more optical barriers 460 may be placed about theperiphery of the light grid 450. The optical barriers is 460 may be madeof, or coated with, a material or substance which does not reflecteither of the beacons 444, 448, for example, the optical barrier 460representatively illustrated in FIG. 13 may have a matte black finishapplied thereto, so that a portion of the beacon 444 which does notstrike the object 418 will not be reflected back to the mirror 442.

Other methods of enhancing the ability of the optical digitizer 420 toaccurately detect the object 418 may be utilized without departing fromthe principles of the present invention. Referring additionally to FIG.14, a lens 462 is positioned in each of the paths of the reflectedbeacons 444, 448 in the respective modules 422, 424 between the mirrors438 and detectors 464 of the light sensors 452. In this manner, thebeacons 444, 448 are focused on the detectors 464, so that only desiredportions of the reflected beacons are within a produced depth of field.

In FIG. 14, the lens 462 of the module 422 focuses the reflected beacon444 on the detector 464 so that the depth of field is approximatelybetween the dashed lines 466 and 468. Similarly, the lens 462 of themodule 424 focuses the reflected beacon 448 on its correspondingdetector 464, so that the depth of field is approximately between thedashed lines 470 and 472. These depths of field, indicated approximatelyby the lines 466, 468, 470, 472 limit the effective light grid 450produced by the overlapping beacons 444, 448. Thus, in FIG. 14, theeffective light grid 450 is between the lines 466 and 468, and betweenlines 470 and 472.

To more clearly describe the use of the lenses 462 in the opticaldigitizer 420, the object 418 is representatively illustrated in threepositions 418a, 418b, 418c with respect to the effective light grid 450.Correspondingly, the beacon 444 is shown in three positions 444a, 444b,444c being reflected off of the object 418, and the beacon 448 is shownin three positions 448a, 448b, 448c also being reflected off of theobject.

With the object 418 at position 418a, it is between the lines 466 and468 and, therefore, is within the depth of field of the module 422. Theobject at position 418a is also between the lines 470 and 472, withinthe depth of field of the module 424. The object at position 418a is,thus, within the effective light grid 450 and its position may be easilydetermined as described hereinabove.

With the object 418 at position 418b, however, it is between the lines470 and 472, within the depth of field of the module 424, but it is notbetween the lines 466 and 468 and, therefore, is not within the depth offield of the module 422. Thus, the module 422 will not detect areflection of the beacon 444 off of the object at position 418b and theobject is outside of the effective light grid 450. In this case, theposition of the object 418 will not be determined.

With the object 418 at position 418c, it is not between the lines 466and 468, nor is it between the lines 470, 472. Therefore, neither of themodules 422, 424 will detect reflections of the respective beacons 444,448 off of the object 418 and the object is outside of the effectivelight grid 450. The position of the object 418 will also not bedetermined by the optical digitizer 420.

Thus, by creating overlapping depths of field using the lenses 462, thelight grid 450 may be effectively limited to a desired area. In thismanner, extraneous objects positioned outside of the effective lightgrid 450 will not cause the optical digitizer 420 to erroneouslydetermine their positions. It will be readily appreciated by one ofordinary skill in the art that the lenses 462 may be otherwisepositioned, and that other lenses, such as the lenses 456, may be usedin combination with the lenses 462 in the optical digitizer 420.

The detectors 464 in the optical digitizer 420 as shown in FIG. 14 maybe of the imaging type (such as a charge coupled device) or non-imagingtype (such as a photodiode). Where the detectors 464 are of thenon-imaging type, the lenses 456 may not be used in the opticaldigitizer 420.

Of course, modifications, substitutions, additions, deletions, and otherchanges may be made to the embodiments of the present inventiondescribed herein which changes would be obvious to one of ordinary skillin the art. Accordingly, the foregoing detailed description is to beclearly understood as being given by way of illustration and exampleonly, the spirit and scope of the present invention being limited solelyby the appended claims.

What is claimed is:
 1. A method of optically determining an object'sposition, the method comprising the steps of:producing a light gridincluding at least two beacons; disposing the object within the lightgrid; reflecting each of the at least two beacons off of the object tothereby produce corresponding at least two reflected beacons; andreceiving each of the at least two reflected beacons into a respectiveone of at least two light sensors.
 2. The method according to claim 1,wherein the producing step further comprises generating at least twolight beams and sweeping the at least two light beams across an area toform the at least two beacons.
 3. The method according to claim 2,wherein the generating step further comprises generating each of the atleast two light beams from a respective one of at least two lightsources.
 4. The method according to claim 2, further comprising thesteps of passing each of the at least two light beams through arespective one of at least two beam splitters.
 5. The method accordingto claim 4, further comprising the step of reflecting each of the atleast two reflected beacons off of a respective one of the at least twobeam splitters and to a respective one of the light sensors.
 6. Themethod according to claim 2, wherein the sweeping step further comprisesreflecting each of the at least two light beams off of a respective oneof at least two mirrors.
 7. The method according to claim 6, wherein inthe sweeping step, each of the at least two mirrors is oscillated. 8.The method according to claim 1, further comprising the step ofdisposing a lens in the optical path of at least one of the at least tworeflected beacons to thereby focus the one of the at least two reflectedbeacons on the respective one of the at least two light sensors.
 9. Themethod according to claim 8, wherein the lens disposing step furthercomprises producing a depth of field of the focused one of the at leasttwo reflected beacons.
 10. The method according to claim 1, furthercomprising the step of disposing a non-reflective material about aperiphery of the light grid.
 11. The method according to claim 1,further comprising the step of disposing a lens in the optical path ofat least one of the at least two reflected beacons to thereby limit aselected one of a width and a height of the at least one of the at leasttwo reflected beacons received into the respective one of the at leasttwo light sensors.
 12. The method according to claim 11, wherein in thelens disposing step, the lens is a generally cylindrical asphericallens.
 13. The method according to claim 1, wherein in the receiving stepat least one of the at least two light sensors includes an imagingdetector.
 14. The method according to claim 13, wherein the receivingstep further comprises receiving an image of the object into the imagingdetector when the object is in the light grid.
 15. The method accordingto claim 14, further comprising the step of comparing the image of theobject to a predetermined image characteristic stored in a CPU.
 16. Amethod of determining an object's position, the method comprising thesteps of:providing first and second modules, the first module beingcapable of producing a first beacon and sensing the first beacon when itis reflected off of the object, and the second module being capable ofproducing a second beacon and sensing the second beacon when it isreflected off of the object; positioning the first and second modulesrelative to a surface, so that a light grid is produced overlying thesurface; reflecting the first and second beacons off of the object; andsensing the reflected first and second beacons.
 17. The method accordingto claim 16, wherein in the positioning step, the surface is an uppersurface of a computer keyboard, and wherein the light grid is positionedabove, and spaced apart from, keys of the keyboard.
 18. The methodaccording to claim 16, further comprising the step of timing thereflected first and second beacons to thereby determine an angularorientation of the object relative to each of the first and secondmodules.
 19. The method according to claim 16, wherein the sensing stepfurther comprises sensing first and second images of the object fromrespective ones of the first and second reflected beacons.
 20. Themethod according to claim 16, further comprising the step of limiting adepth of field of the first module.
 21. The method according to claim20, wherein the limiting step is performed by disposing a lens in theoptical path of the reflected first beacon.
 22. The method according toclaim 21, wherein the lens is not disposed in the optical path of thefirst beacon before the first beacon is reflected off of the object. 23.The method according to claim 16, further comprising the step oflimiting a dimension of the first reflected beacon sensed by the firstmodule.
 24. The method according to claim 23, wherein the limiting stepis performed by disposing a lens in the optical path of the reflectedfirst beacon.
 25. The method according to claim 23, wherein in thelimiting step, a selected one of a height and a width of the firstreflected beacon is limited.
 26. Apparatus for optically determining anobject's position relative to a surface, the apparatus comprising:firstand second beacon generators positioned relative to the surface; andfirst and second light sensors, each of the first and second lightsensors being disposed relative to a respective one of the first andsecond beacon generators, so that a first beacon produced by the firstbeacon generator and reflected off of the object is receivable by thefirst light sensor, and a second beacon produced by the second beacongenerator and reflected off of the object is receivable by the secondlight sensor, the apparatus being free of reflective material forreflecting any portions of the first and second beacons that are notreflected off of the object to the first and second light sensors. 27.The apparatus according to claim 26, further comprising a lens disposedrelative to the first light sensor, the lens being capable of focusingthe first beacon on the first light sensor when the first beacon hasbeen reflected off of the object.
 28. The apparatus according to claim26, further comprising a lens disposed relative to the first beacongenerator, the lens being capable of limiting a dimension of the firstbeacon received by the first light sensor when the first beacon has beenreflected off of the object.
 29. The apparatus according to claim 26,wherein the first light sensor includes an imaging detector.
 30. Acomputer system for optically determining an object's position, thecomputer system comprising:a monitor; a central processing unitinterconnected to the monitor; a surface relative to which the object'sposition is to be determined; first and second beacon generatorspositioned relative to the surface; and first and second light sensorsinterconnected to the central processing unit, each of the first andsecond light sensors being disposed relative to a respective one of thefirst and second beacon generators, so that a first beacon produced bythe first beacon generator and reflected off of the object is receivableby the first light sensor, and a second beacon produced by the secondbeacon generator and reflected off of the object is receivable by thesecond light sensor, the computer system being free of reflectivematerial for reflecting any portions of the first and second beaconsthat are not reflected off of the object to the first and second lightsensors.
 31. The computer system according to claim 30, furthercomprising a lens disposed relative to the first light sensor, the lensbeing capable of focusing the first beacon on the first light sensorwhen the first beacon has been reflected off of the object.
 32. Thecomputer system according to claim 30, further comprising a lensdisposed relative to the first beacon generator, the lens being capableof limiting a dimension of the first beacon received by the first lightsensor when the first beacon has been reflected off of the object. 33.The computer system according to claim 30, wherein the first lightsensor includes an imaging detector.
 34. The computer system accordingto claim 30, wherein the surface is an upper surface of a keyboardinterconnected to the central processing unit.